The present invention relates generally to video signal, speed-change reproducing systems, and more particularly to a video signal, speed-change reproducing system for reproducing signals recorded on mutually adjacent tracks, alternately by means of two heads having mutually different azimuth angles and mutually different track widths. The video signal may thus be reproduced at a speed which is different from that used for making the recording.
The prior art uses a system wherein a video signal is recorded on a magnetic tape on parallel tracks formed obliquely relative to the longitudinal direction of the magnetic tape. This tape travels at a speed which is different from that used at the time of recording. Or, the tape may stop. Thus, the tape transport provides a speed-change reproduction such as quick-motion reproduction, slow-motion reproduction, or still picture reproduction. In this system, the tape speed at the time of reproduction is different from that at the time of recording; therefore the path (track) which the head traces on the tape during reproduction is different from the path (track) traced by the head during recording.
On the one hand, a conventional video signal recording and reproducing system, ordinarily, forms tracks on a recording medium in a manner which leaves an unrecorded zone or band called a guard band between neighboring tracks, in order to prevent the generation of beats caused by the reproduced signals of neighboring tracks due to tracking deviation of the head at the time of reproduction. When a tape recorded in this manner is played back at a speed-change reproduction, as described above, the head traces over the track and the unrecorded band. When the head traces over the unrecorded band, the level of the reproduced signal is lowered remarkably or it disappears. For this reason, noise is generated in the reproduced picture. Furthermore, in the above mentioned system, the unrecorded bands between tracks give a poor utilization efficiency of the tape.
In addition, there has been a system wherein the angle of inclination of the tape, relative to the head rotating plane, is varied in accordance with the tape speed so that the heads will trace accurately over the track at the time of speed-change reproduction. However, this system has been accompanied by the twin problems of the complexity of the mechanism for varying the inclination angle of the tape, which gives rise to high cost of the apparatus, and by the difficulty of accurately tracking in actual practice.
On the other hand, a system wherein tracks are formed on a tape without gaps between neighboring tracks has been previously proposed. Moreover a color video signal can be recorded and reproduced without the occurrence of beat disturbance. Please see the U.S. patent application Ser. No. 731,935 entitled "Color video signal recording and/or reproducing system" filed Oct. 13, 1976, by Akira Hirota, inventor, and assigned to Victor Company of Japan, Ltd., the same assignee of the present invention, now U.S. Pat. No. 4,178,606. In this previously described system, a pair of azimuth heads have gaps which are inclined, with a certain azimuth angle, in mutually opposite directions with respect to the direction perpendicular to the longitudinal direction of the track. Neighboring tracks are formed in contiguous contact, side-by-side relationship without a gap therebetween. Furthermore, the phase of the chrominance signal is shifted by 90 degrees for every horizontal scanning period. Moreover, the direction of this phase shifting Further, accordance with this system, the tape utilization efficiency is high since the tracks are in close contact with each other, and, moreover, there is no occurrence of beat disturbance.
Accordingly, the present applicant has previously a novel and useful system has been previously proposed for speed-change reproduction of video signals, which system is effectively applicable particularly to the above mentioned previously proposed system, and in which the above described difficulties have been overcome, in the U.S. patent application Ser. No. 892,147 entitled "Video signal speed-change reproducing system" filed Mar. 31, 1978, by Akira Hirota, inventor, and assigned to Victor Company of Japan, Ltd., the same assignee of the present invention, now abandoned.
In this system, by selecting the tape speed at a specific value at the time of reproduction, the noise bar is always produced at a certain position on the picture screen. Furthermore, if the relative scanning phases of the heads on the tape have a specific relationship to the tape, the noise bar can be positioned at an inconspicuous or invisible position on the picture screen. Furthermore, by using heads having mutually different azimuth angles and different track widths, signal reproduction can be carried out so that the reproduced signal level does not become zero. The vertical synchronizing signal is reproduced even when the reproduced signal level becomes a minimum. The vertical synchronization can be positively obtained even when a noise bar is produced due to the minimum reproduced signal level, within a vertical blanking period.
However, this described system has the problem that it is necessary to change over the tracking adjustment in response to changes of the tape speed, so that the heads can start reproducing from a desired position on the track.